conventional log saws and especially hardwood saws of about 48" to 54" in diameter are made of circular high strength steel plate having a thickness of 6 AWG (0.194") at the centre, and 7 AWG (0.179") at the rim. A "welded on" or "interchangeable" tooth on these saws has a typical width of 0.312". Accordingly, and adding normal wobbling of the saw, a width of cut, or the kerf of a saw, of between 0.450" to 0.480" was considered satisfactory.
During the last few years, substantial efforts have been made to reduce the kerf of a saw, as a means to recover more lumber from every log. Thin saws having a throughout plate thickness of 8 AWG, (0.164"), and a tooth width of 0.261" have been introduced to the industry. However, without a good guiding system the thin-kerf saw is easier deflected, and the width of cut remains unchanged.
One example of a guiding system for thin-kerf saws is found in the disclosure of U.S. Pat. No. 5,213,020 issued May 25, 1993 to Pleau et al. This guiding system is used on large head saws which are held at a fixed location on a driving mandrel. The guiding system uses three sets of wear plugs mounted on a "C"-block at the in-feed side of the saw. Each set of wear plugs consists of two cylindrical blocks facing one another and each being at a specific clearance from a respective side of the saw plate. Further-more, two sets of wear plugs are spaced apart circumferentially a distance equal to a length of one gullet plus one tooth width. A third set of wear plugs is placed radially inwardly to the top first set at about 1/3 of the distance from a tooth gullet to the centre of the blade. This guiding system is used to maintain a proper alignment of the saw during sawing and to prevent buckling near a gullet of a tooth.
Another arrangement which belongs to the state of the art is known in the trade as a Floating Guide System. An example of this Floating Guide System may be found in the 1993 Catalogue of Pacific/Hoe, located in Portland, Oreg., U.S.A. Such Floating Guide System is on sale to the sawmill industry since at least October 1990. The guide system is used on either a fixed head saw or on a saw which floats axially on a driving mandrel.
The Floating Guide System uses 3 sets of grill pads. Each set consists of two pads, facing one another, and at a specific clearance from a respective side of the saw plate. Two arm members, at the in-feed side of the saw and each projecting inwardly parallel to a respective side of the saw maintain the two in-feed sets of pads at a distance of 20" from one another, and at a same radial distance from the centre of the saw. A third set of pads is similarly mounted at the out-feed side of the saw, below the line of cut, and at the same radial distance as the in-feed pads. This 20" spacing of the in-feed pads is intended to increase a span between integral supporting surfaces to prevent a slanting of the saw.
It has been found by experience that despite the previously taught spacings for the in-feed guide pads, the width of cut is not always reduced significantly.
Another problem with prior art guide systems is related to the lubrication of guide pads. It has been a common practice to introduce lubricant between the pad and the saw blade, through an opening at the centre of the pad. As the blade turns, the lubricant is inevitably carried to the out-feed side of the pad, resulting in an uneven distribution of the lubricant and in a premature wear on the leading side of the pad. Such uneven wear causes uneven pad contact with the saw, and a consequential loss of efficiency of the guiding system. An example of such lubrication system is disclosed in Canadian Patent No. 870,393, issued May 11, 1971 to Fairfield et al.
A similar problem of uneven pad contact with prior art systems is caused by a lack of adjustment on the guiding pads. Such devices are not always mounted under ideal working conditions. The installation often requires welding to working or bent structural members, or bolting into oversized holes or on rough surfaces. Hence, the pads are not always in perfect alignment with the saw, and a performance of the guide system is likewise reduced.